Boiling-up time

The latest innovation is the further development of the material to produce the new Ceran Suprema glass-ceramic cooktop panel. Optimization of the composition of the material plus a new manufacturing process resulted in a further improvement of the heat transmission and temperature resistance of the glass ceramic. In consequence, built-in radiant heating elements can now be adjusted to higher cooking zone temperatures. And boil-up time, depending on the cookware used, can be as much as 20% less (see also Sect. 3.2.3). 

Besides the right choice and placement of cookware, there are further factors that influence boil-up times and therefore the technical performance of the cooking system. These are ... 

Once a minimum reflux has been established (which is not an operating condition), then a realistic reflux ratio of from 1.5 to as much as 10 times the minimum can be selected. Of course, the larger the reflux value down the column the more vapor has to be boiled up, and the greater will be the required column diameter. So, some economic balance must be determined. 

The still provides a constant vapour boil-up rate, which remains constant with respect to time. 

Benzyl cyanide (40 g. = 0 33 mole) is heated in a round-bottomed flask (capacity 0-5 1.), with a mixture of 50 c.c. of concentrated sulphuric acid and 30 c.c. of water. The flask is provided with an upright air condenser, and is placed in a conical (Babo) air bath. The heating is continued until the appearance of small bubbles of vapour indicates that a reaction, which rapidly becomes violent, has set in the liquid boils up, and white fumes are emitted. It is allowed to cool and then two volumes of water are added. After some time the phenylacetic acid which has crystallised out is filtered off with suction. If a sample of the material does not form a clear solution with sodium carbonate in water (presence of phenylacetamide), the whole of the crude material is shaken with sodium carbonate solution and the mixture is filtered. From the clear filtrate phenylacetic acid is reprecipitated with sulphuric acid, and can be recrystallised directly from a rather large volume of hot water or, after drying, from petrol ether. Because of its low melting point (76°) it often separates at first as an oil, but it can also be conveniently purified by distillation in vacuo from a sausage flask.2... 

These combined fractions (which boil up to 210°) and 15 g. of sodium are placed in a 2-1. distilling flask, the side-arm of which is closed with a rubber tube and pinchcock and which is fitted with a reflux condenser. The mixture is heated just below the boiling point for about three hours, during which time the impurities are attacked by the molten sodium, and a gelatinous, reddish mass forms. The reflux condenser is now removed and one set for downward distillation is attached to the side-arm. The mixture is distilled, and about two-thirds of the liquid... 

The properties of a fractionating column which are important for isotope separation are (1) the throughput or boil-up rate which determines production (2) HETP (height equivalent per theoretical plate) which determines column length (3) the hold-up per plate which determines plant inventory and time to production (4) the pressure drop per plate which should be as small as possible. The choice of a particular column is invariably a compromise between these factors. The separation in a production column is of course less than it would be at total reflux (no product withdrawal). The concentration at any point in the enriching section can be calculated from the transport equation (see, e.g., London 1961)... 

Transient Heating of Droplets When a cold liquid fuel droplet is injected into a hot stream or ignited by some other source, it must be heated to its steady-state temperature Ts derived in the last section. Since the heat-up time can influence the V/2 law, particularly for high-boiling-point fuels, it is of interest to examine the effect of the droplet heating mode on the main bulk combustion characteristic—the burning time. 

C) Preparation of 9,10-Dihydro-4H-Benzo[4,5]Cyclohepta[l,2-b]Thiophen-(4)-One 200 ml of 85% phosphoric acid and 112 g of phosphorus pentoxide are heated to 135°C. 7.0 g of o-[2-thienyl-(2 )-ethyl]benzoic acid are then introduced while stirring thoroughly over a period of 30 min. Stirring is then continued for another hour at 135°C and the reaction mixture is then stirred into 1 liter of ice water. Extraction is then effected 3 times, using 250 ml ether portions, the ethereal extract is washed with 2 N sodium carbonate solution, dried over sodium sulfate and reduced in volume by evaporation. The residue is boiled up with 55 ml of ethanol, the solution freed of resin by decanting and then stirred at room temperature for 6 hours with animal charcoal. It is then filtered off, reduced in volume in a vacuum and the residue distilled. BP 120° to 124°C/0.005 mm, nD24-5 = 1.6559. 

Table 5.2 summarises the results for two cases (i) constant vapour boil-up rate, (ii) variable vapour boilup rate. The initial and final time optimal reflux ratio values are shown in Table 5.2 for both cases. The optimal reflux ratios between these two points follow according to Equation P.13 for each case. See details in the original reference (Robinson, 1969). 

Two binary mixtures are being processed in a batch distillation column with 15 plates and vapour boilup rate of 250 moles/hr following the operation sequence given in Figure 7.7. The amount of distillate, batch time and profit of the operation are shown in Table 7.6 (base case). The optimal reflux ratio profiles are shown in Figure 7.8. It is desired to simultaneously optimise the design (number of plates) and operation (reflux ratio and batch time) for this multiple separation duties. The column operates with the same boil up rate as the base case and the sales values of different products are given in Table 7.6. 

However, most of the batch distillation models (e.g. Mujtaba and co-workers Sorensen and Skogestad, 1996) relate the amount of distillate collected (Hamodei) with the vapour boil-up rate in the column (Vtomm), the internal reflux ratio (Rmodei) and the total operating time (tdig) by,... 

How much time would be required to obtain some specific product composition at some constant boil-up rate, or what boil-up rate would be required to obtain some specific product composition within some specified time under conditions of,... 

Because the boil-up rate associated with a specific distillation system should be known from past experience with the system, this calculation of total vapor load immediately produces a time required for the new separation. 

Conversely, in the design of a new system, the time available for the distillation can be divided into the vapor load to determine the boil-up rate required. 

As noted under the discussion of the coustant reflux ratio case, the boil-up rate of an existing distillation system should be well known, so use of that boil-up rate with the vapor quantity just calculated will yield the time required for the separation of the new system. Note that this value of time refere only to the distillation itself charging time, heat-up time, cooling time and clean-out time are not included. 

The volatile peroxides, other oxidation decomposition products, and odiferous compounds form reduced-boiling point azeotropes with water in the steam, at high temperatures, 250-260°C/482-500°F, and very low absolute pressures ( 3 mbar). This is above the smoke point of soybean oil, but below the flash point, and oxygen must be excluded. Considerable heat bleaching of yellow-red carotenoids also occurs at this temperature. Typically the deodorization process requires 20-40 min after come-up time, uses 0.5-2.0 percent spaiged steam (the higher level if tocopherols are recovered), operates at between 2 and 4 mbar, and produces a product with about 0.03-0.05 percent FFA.143... 

The main tank is filled with liquid hydrogen from a trailer. Despite the sophisticated heat insulation in any container for cryogenic liquids, the small amount of remaining heat input vfill trigger off a warming process in the tank which causes the liquid in the container to evaporate and the pressure to rise. After a certain pressure build-up time the maximum operating pressure of the tank is reached. The pressure relief valve has to be opened. From this point onwards, gas must be released (boil-off). The container now acts as an open system with gas usually being lost to the environment. 

In order to simulate the pressure increase and pressure build-up time in the storage system, we shall first assume a closed system in thermodynamic equilibrium with a constant heat input Q, see Figure 1.11. We assume that the pressure and temperature of the boiling liquid hydrogen and the gaseous saturated hydrogen vapor are the same throughout the whole system. 

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